[Mellanox] Support UID LED in platform API (#11592)

- Why I did it
As a LED indicator to help user to find switch location in the lab, UID LED is a useful LED in Mellanox switch.

- How I did it
I add a new member _led_uid in Mellanox/Chassis.py, and extend Mellanox/led.py to support blue color.
Relevant platform-common PR sonic-net/sonic-platform-common#369

- How to verify it
Add unit test cases in test.py, and do manual test including turn-on/off/show uid led.

Signed-off-by: David Xia <daxia@nvidia.com>

platform/mellanox/mlnx-platform-api/sonic_platform/chassis.py

@@ -75,6 +75,9 @@ class Chassis(ChassisBase):
     # System status LED
     _led = None
 
+    # System UID LED
+    _led_uid = None
+
     def __init__(self):
         super(Chassis, self).__init__()
 
@@ -622,8 +625,10 @@ class Chassis(ChassisBase):
 
     def initizalize_system_led(self):
         if not Chassis._led:
-            from .led import SystemLed
+            from .led import SystemLed, \
+                SystemUidLed
             Chassis._led = SystemLed()
+            Chassis._led_uid = SystemUidLed()
 
     def set_status_led(self, color):
         """
@@ -650,6 +655,31 @@ class Chassis(ChassisBase):
         self.initizalize_system_led()
         return None if not Chassis._led else Chassis._led.get_status()
 
+    def set_uid_led(self, color):
+        """
+        Sets the state of the system UID LED
+
+        Args:
+            color: A string representing the color with which to set the
+                   system UID LED
+
+        Returns:
+            bool: True if system LED state is set successfully, False if not
+        """
+        self.initizalize_system_led()
+        return False if not Chassis._led_uid else Chassis._led_uid.set_status(color)
+
+    def get_uid_led(self):
+        """
+        Gets the state of the system UID LED
+
+        Returns:
+            A string, one of the valid LED color strings which could be vendor
+            specified.
+        """
+        self.initizalize_system_led()
+        return None if not Chassis._led_uid else Chassis._led_uid.get_status()
+
     def get_watchdog(self):
         """
         Retrieves hardware watchdog device on this chassis

platform/mellanox/mlnx-platform-api/sonic_platform/led.py

@@ -28,10 +28,12 @@ class Led(object):
     STATUS_LED_COLOR_GREEN = 'green'
     STATUS_LED_COLOR_RED = 'red'
     STATUS_LED_COLOR_ORANGE = 'orange'
+    STATUS_LED_COLOR_BLUE = 'blue'
     STATUS_LED_COLOR_OFF = 'off'
     STATUS_LED_COLOR_GREEN_BLINK = 'green_blink'
     STATUS_LED_COLOR_RED_BLINK = 'red_blink'
     STATUS_LED_COLOR_ORANGE_BLINK = 'orange_blink'
+    STATUS_LED_COLOR_BLUE_BLINK = 'blue_blink'
 
     LED_ON = '255'
     LED_OFF = '0'
@@ -47,7 +49,8 @@ class Led(object):
         'red': 'red',
         'amber': 'red',
         'orange': 'red',
-        'green': 'green'
+        'green': 'green',
+        'blue': 'blue'
     }
 
     LED_PATH = "/var/run/hw-management/led/"
@@ -273,6 +276,12 @@ class SystemLed(Led):
         self._led_id = 'status'
 
 
+class SystemUidLed(Led):
+    def __init__(self):
+        super().__init__()
+        self._led_id = 'uid'
+
+
 class SharedLed(object):
     # for shared LED, blink is not supported for now. Currently, only PSU and fan LED
     # might be shared LED, and there is no requirement to set PSU/fan LED to blink status.

platform/mellanox/mlnx-platform-api/tests/test_led.py

@@ -44,6 +44,13 @@ class TestLed:
         assert physical_led is not None
         self._verify_non_shared_led(physical_led, chassis)
 
+    def test_uid_led(self):
+        chassis = Chassis()
+        assert chassis.set_uid_led('blue') is False
+        physical_led = chassis._led_uid
+        assert physical_led is not None
+        self._verify_uid_led(physical_led, chassis)
+
     def _verify_non_shared_led(self, physical_led, obj):
         mock_file_content = self._mock_led_file_content(physical_led)
 
@@ -84,18 +91,39 @@ class TestLed:
         mock_file_content[physical_led.get_led_delay_off_path('green')] = Led.LED_OFF
         mock_file_content[physical_led.get_led_delay_on_path('green')] = Led.LED_OFF
 
+    def _verify_uid_led(self, physical_led, obj):
+        mock_file_content = self._mock_led_file_content(physical_led)
+
+        def mock_read_str_from_file(file_path, **kwargs):
+            return mock_file_content[file_path]
+
+        def mock_write_file(file_path, content, **kwargs):
+            mock_file_content[file_path] = content
+
+        utils.read_str_from_file = mock_read_str_from_file
+        utils.write_file = mock_write_file
+
+        assert obj.get_uid_led() == Led.STATUS_LED_COLOR_GREEN
+        mock_file_content[physical_led.get_led_path('green')] = Led.LED_OFF
+        assert obj.set_uid_led(Led.STATUS_LED_COLOR_BLUE) is True
+        assert obj.get_uid_led() == Led.STATUS_LED_COLOR_BLUE
+        mock_file_content[physical_led.get_led_path('blue')] = Led.LED_OFF
+
     def _mock_led_file_content(self, led):
         return {
             led.get_led_path('green'): Led.LED_ON,
             led.get_led_path('red'): Led.LED_OFF,
             led.get_led_path('orange'): Led.LED_OFF,
-            led.get_led_cap_path(): 'none green green_blink red red_blink orange',
+            led.get_led_path('blue'): Led.LED_OFF,
+            led.get_led_cap_path(): 'none green green_blink red red_blink orange blue',
             led.get_led_delay_off_path('green'): Led.LED_OFF,
             led.get_led_delay_on_path('green'): Led.LED_OFF,
             led.get_led_delay_off_path('red'): Led.LED_OFF,
             led.get_led_delay_on_path('red'): Led.LED_OFF,
             led.get_led_delay_off_path('orange'): Led.LED_OFF,
             led.get_led_delay_on_path('orange'): Led.LED_OFF,
+            led.get_led_delay_off_path('blue'): Led.LED_OFF,
+            led.get_led_delay_on_path('blue'): Led.LED_OFF,
         }
 
     @mock.patch('sonic_platform.led.Led._wait_files_ready', mock.MagicMock(return_value=True))